Manufacturing method of electronic device package, electronic device package, and oscillator

ABSTRACT

An electronic device package manufacturing method includes: forming a metal film on both surfaces of the cover substrate so that the metal film on one surface and the metal surface on the other surface conduct with each other; aligning and superimposing the cover substrate and the base substrate; and bonding the base substrate and the cover substrate together via the metal film by anodic bonding by bringing a negative electrode plate into contact with the base substrate on an entire surface opposite to a surface bonded to the cover substrate, bringing a positive electrode plate into contact with the cover substrate on an entire surface opposite to a surface bonded to the base substrate, and applying a voltage between the positive and negative electrode plates. The base substrate and the cover substrates can be thus bonded together via the metal film by anodic bonding in a stable manner.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. 2010-049878 filed on Mar. 5, 2010, the entire content ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a package for a surface mount device(SMD) in which an electronic device is encapsulated in a cavity formedbetween two substrates bonded together, and more particularly, to astructure to bond two substrates by anodic bonding.

2. Description of the Related Art

Recently, electronic devices using a compact surface mount devicepackage are employed often in mobile phones and personal digitalassistants. Of these electronic devices, many components, such as atransducer, an MEMS, a gyrosensor, and an acceleration sensor, require apackage of a hollow cavity structure. A structure in which an insulatorbase substrate and an insulator cover substrate are bonded together viaa metal film is known as a package of the hollow cavity structure. Also,eutectic bonding, seam bonding, and anodic bonding are known as abonding method. Details are described, for example, in JP-A-09-002845.

A manufacturing method of a package in the related in which an insulatorbase substrate and an insulator cover substrate are bonded together viaa metal film by anodic bonding will now be described. In particular, adescription will be given to a manufacturing method by which a pluralityof package elements are formed in array on a single sheet of basesubstrate and after a cover substrate is bonded to the base substrate,the bonded substrates are divided into individual packages.

As are shown in FIG. 8A through FIG. 8E, an electronic device package inthe related art includes an electronic device 47, a base substrate 41provided with a concave portion, a plate-shaped cover substrate 42, anda metal film 49, which is a bonding film to bond the base substrate 41and the cover substrate 42 together. Because the base substrate 41 isprovided with a concave portion, a cavity 46 is formed by sealing thebase substrate 41 with the cover substrate 42. The electronic device 47is accommodated in the cavity 46.

The base substrate 41 is formed of an insulator containing movable ions,for example, a glass material, and formed to have concave portions.Wires 43 used to mount the electronic devices 47 are formed on thesurface of the base substrate 41 in a number according to the number ofthe electronic devices 47 to be mounted. Outside electrodes 45 areformed on the back surface of the base substrate 41 in a correspondingmanner to the wires 43. In order to connect the wires 43 on the frontsurface of the base substrate 41 and the corresponding outsideelectrodes 45 on the back surface, through-holes are formed at arbitraryportions of the packages and feed-through electrodes 44 are formed tofill the respective through-holes. The wires 43 and the outsideelectrodes 45 are thus connected via the feed-through electrodes 44.

As with the base substrate 41, the cover substrate 42 is formed of aninsulator containing movable ions, such as a glass material and formedin a plate shape. When the cavities 46 are formed as the base substrate41 and the cover substrate 42 are bonded together, the metal film 49 isformed as the bonding film in a portion where the base substrate 41 andthe cover substrate 42 come into contact with each other. Basically, itis sufficient to form the metal film 49 only on the portion where thebase substrate 41 and the cover substrate 42 come into contact with eachother. However, by taking simplification of the steps into account, asis shown in FIG. 8D, the metal film 49 is formed entirely on one surfaceof the cover substrate 42.

The manufacturing method will now be described. A plurality of concavecavities 46 are formed in a wafer of base substrate 41 so that aplurality of electronic devices 47 can be mounted thereon. Thereafter,the wires 43 used to mount the electronic devices 47, the outsideelectrodes 45, and the feed-through electrodes 44 are formed (FIG. 8A).Subsequently, the electronic devices 47 are mounted in the cavities 46and the electronic devices 47 and the wires 43 are connected with wires48 by wire bonding (FIG. 8B). On one surface of the plate-shaped coversubstrate 42 (FIG. 8C), the metal film 49 as a bonding film is formed(FIG. 8D). Aluminum, chrome, silicon, and copper are suitable as themetal film.

The base substrate 41 and the cover substrate 42 are aligned andsuperimposed, and then bonded together by anodic bonding. When bondedtogether by anodic bonding, as is shown in FIG. 8E, the base substrate41 and the cover substrate 42 aligned with each other are sandwiched bysubstrates 50 and 51 serving as heaters and also as electrodes. Apositive electrode probe 52 is set so as to come into contact with themetal film 49 and temperatures of the substrates 50 and 51 serving asheaters and electrodes are raised. A voltage is then applied between thepositive electrode probe 52 and the substrate 50 serving as a heater andan electrode. Consequently, the base substrate 41 and the coversubstrate 42 are bonded together via the metal film 49. Thereafter,package elements are cut off individually using a dicing apparatus orthe like. Individual electronic device packages are thus completed.

The manufacturing method of the electronic device package in the relatedart, however, has problems as follows. Firstly, the positive electrodeprobe 52 is brought into contact with a part of the metal film 49, whichis a bonding film, when anodic bonding is performed. In this instance,in a case where the metal film 49 has high sheet resistance, it isdifficult to maintain the entire surface of the cover substrate 42,which is a wafer, at the same potential. This poses a problem thatbonding strength varies within the wafer plane. As a countermeasure tolower the sheet resistance, the resistance value is decreased by makingthe metal film 49 thicker. However, when the metal film 49 becomesthicker, bonding strength between the metal film 49 and the basesubstrate 41 becomes lower. Further, because the metal film 49 is formedon one surface of the cover substrate 42, when the metal film 49 becomesthicker, there arises another problem that the cover substrate 42 warps.

In addition, in order to bring the positive electrode probe 52 intocontact with a part of the metal film 49, as is shown in FIG. 8E, itbecomes necessary to displace the base substrate 41 and the coversubstrate 42 from each other for the positive electrode probe 52 to comeinto contact with a part of the metal film 49. This poses anotherproblem that alignment of the base substrate 41 and the cover substrate42 is limited strictly. In particular, in the case of a package in whicha pattern is formed on the cover substrate 42, there is a problem thatthe limitation on alignment gives considerable influences to the numberof products taken out from the wafer.

SUMMARY OF THE INVENTION

The invention was devised in view of the foregoing and has an object toprovide a manufacturing method of an electronic device package capableof bonding an insulator base substrate and an insulator cover substratetogether via a metal film by anodic bonding in a stable manner.

A manufacturing method of an electronic device package according to anaspect of the invention is a manufacturing method of an electronicdevice package including a base substrate formed of an insulatorcontaining movable ions, a cover substrate formed of an insulatorcontaining movable ions and bonded to the base substrate while beingopposed to the base substrate, and electronic devices respectivelyaccommodated in a plurality of cavities formed between the basesubstrate and the cover substrate and mounted on the base substrate. Themanufacturing method includes: forming a metal film on both surfaces ofthe cover substrate so that the metal film on one surface and the metalsurface on the other surface conduct with each other; aligning andsuperimposing the cover substrate and the base substrate; and bondingthe base substrate and the cover substrate together via the metal filmby anodic bonding by bringing one electrode plate into contact with thebase substrate on a surface opposite to a surface bonded to the coversubstrate, bringing the other electrode plate into contact with thecover substrate on a surface opposite to a surface bonded to the basesubstrate, and applying a voltage between the one electrode plate andthe other electrode plate.

According to the manufacturing method of an electronic device package ofthe invention, the metal film is formed on the both surfaces of a waferfrom which the cover substrate is formed in such a manner that the metalfilm on one surface and the metal film on the other surface conduct witheach other. It thus becomes possible to bring the electrode plate intocontact with the cover substrate on the surface opposite to the surfacebonded to the base substrate. Accordingly, there can be achieved anadvantage that potential in the bonding portion can be maintained in areliable manner. The invention is particularly effective when metalhaving high sheet resistance is used as a material of the metal film oran extremely thin metal film is used. In addition, in a case where metalhaving high sheet resistance is used as a material of the metal film,the need to make the metal film thicker is eliminated. This makes itpossible to prevent warping of the cover substrate caused by the metalfilm. Hence, there can be achieved an advantage that alignment accuracyof the base substrate and the cover substrate is enhanced. Moreover,because the electrode plate can be brought into contact with the coversubstrate on the surface opposite to the surface bonded to the basesubstrate, the alignment of the base substrate and the cover substrateis no longer limited strictly.

Further, by bringing the electrode plate into contact with the coversubstrate on the entire surface opposite to the surface bonded to thebase substrate during anodic bonding, not only does it become possibleto achieve an advantage of the metal film covering the cover surface,but it also becomes possible to achieve an advantage of interchange ofcharges that depends on the capacity of the cover substrate, which is aninsulator. Consequently, an amount of charges migrating during anodicbonding is increased. This results in an advantage that further higherbonding strength can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing one embodiment of an electronicdevice package of the invention;

FIG. 2 is a cross section showing one embodiment of the electronicdevice package of the invention;

FIG. 3 is a flowchart depicting one embodiment of a manufacturing methodof the electronic device package of the invention;

FIG. 4A through FIG. 4E are cross sections of a flowchart depicting oneembodiment of the manufacturing method of the electronic device packageof the invention;

FIG. 5A and FIG. 5B are cross sections of the flowchart depicting oneembodiment of the manufacturing method of the electronic device packageof the invention;

FIG. 6 is a cross section showing another embodiment of the electronicdevice package of the invention;

FIG. 7 is a view showing one embodiment of an oscillator of theinvention; and

FIG. 8A through FIG. 8E are cross sections of a flowchart depicting amanufacturing method of an electronic device package in the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, one embodiment of the invention will be described withreference to FIG. 1 through FIG. 5B. As are shown in FIG. 1 and FIG. 2,an electronic device package 1 of this embodiment is a surface mountdevice package including a base substrate 2 and a cover substrate 3laminated in two layers in a box shape and an electronic device 4accommodated in a cavity 5 formed inside the box. The electronic device4 means an LSI, an MEMS, a sensor, and a piezoelectric transducer, or acomplex thereof.

Both the base substrate 2 and the cover substrate 3 are insulatorscontaining movable ions, for example, insulating substrates made ofsoda-lime glass. In the case shown in FIG. 1 and FIG. 2, a rectangularconcave portion (cavity) 5 large enough to accommodate the electronicdevice 4 is formed in the base substrate 2 and the cover substrate 3 isformed in a plate shape. The concave portion 5 is a concave portion thatlater forms the cavity 5 in which to accommodate the electronic device 4when the both substrates 2 and 3 are superimposed. The base substrate 2is bonded to the cover substrate 3 by anodic bonding via the metal film6, which is a bonding film, in a state where the concave portion 5 isopposed to the cover substrate 3.

As is shown in FIG. 2, feed-through electrodes 9 are formed in the basesubstrate 2 to electrically connect the electronic device 4 and outsideelectrodes 10. Through-holes in which to insert the feed-throughelectrodes 9 are formed to open within the cavity 5. With reference toFIG. 2, descriptions will be given to through-holes that penetratestraight through the base substrate 2 while maintaining substantially aconstant diameter. The invention, however, is not limited to this case.For example, through-holes may be tapered by gradually increasing ordecreasing the diameter toward the bottom surface of the base substrate2. In any case, it is sufficient that through-holes penetrate throughthe base substrate 2.

The feed-through electrodes 9 are formed in the respective through-holesso as to fill the through-holes. The feed-through electrodes 9 play notonly a role of maintaining the interior of the cavity 5 hermetically bycompletely closing the through-holes but also a role of bringing theoutside electrodes 10 and the electric device 4 into conduction. Aclearance between the through-hole and the feed-through electrode 9 iscompletely filled using a glass frit material having a thermal expansioncoefficient adjusted to that of the glass material of the base substrate2.

In this embodiment, a clearance between the through-hole and thefeed-through electrode 9 is filled with a glass frit material. However,the invention is not limited to this configuration and a conductiveadhesive and a resin-based filling material are also available. Aconductive adhesive and a resin-based filling material, however,deteriorate with time or causes the generation of outgas. Hence, fromthe viewpoint of reliability over a long term, a glass frit material ora glass material per se is desirable to fill a clearance between thethrough-hole and the feed-through electrode 9.

A manufacturing method of an electronic device package according to oneembodiment of the invention will now be described with reference to theflowchart of FIG. 3 and FIG. 4A through FIG. 5B.

Initially, the base substrate 2 is obtained by polishing and etching awafer of insulating substrate until it reaches a target thicknessfollowed by rinsing (S10). Subsequently, concave portions that laterform the cavities 5 are formed in the base substrate 2, which is aplate-shaped insulator (S11). The concave portions can be formed by anyappropriate method and etching by photolithography and press working areapplicable. Subsequently, through-holes are formed in the bottoms of thecavities 5. The through-holes can also be formed by any appropriatemethod and etching by photolithography and press working are applicable(S12). Wires 8 used to mount the electronic devices 4 on the bottomsurfaces of the cavities 5 are formed (S13). Subsequently, thefeed-through electrodes 9 are formed in the through-holes formed in thebottoms of the cavities 5 (S14). Further, the outside electrodes 10 areformed on the surface of the base substrate 2 opposite to the bottomsurfaces of the cavities 5 (S15). FIG. 4D shows the base substrate 2 ina state where the outside electrodes 10 have been formed.

Meanwhile, the cover substrate 3 is obtained by polishing and etching awafer of insulating substrate until it reaches a target thicknessfollowed by rinsing (S20). Subsequently, as is shown in FIG. 4B, themetal film 6 as a bonding film is formed on the entire one surface ofthe plate-shaped cover substrate 3 and on the side surfaces of the coversubstrate 3 in the thickness direction (S21). Herein, the metal film 6is formed using methods, such as vapor deposition, sputtering, and CVD.Also, Al, Si, and Cr are used for the metal film 6 and a thicknessthereof is set to a range of 200 angstroms to 2000 angstroms.Subsequently, as is shown in FIG. 4C, the metal film 6 as a bonding filmis formed on the entire other surface of the cover substrate 3 and onthe side surfaces of the cover substrate 3 in the thickness direction(S22). Again, the metal film 6 is formed using methods, such as vapordeposition, sputtering, and CVD. Also, Al, Si, and Cr are used for themetal film 6 and a thickness thereof is set to a range of 200 angstromsto 2000 angstroms. Consequently, the metal film 6 is formed entirely onboth the front and back surfaces of the cover substrate 3 and the metalfilm 6 on the front surface and the metal film 6 on the back surfaceconduct with each other via the metal film 6 formed on the entire sidesurfaces of the cover substrate 3. In short, the substrate 3 is coveredwith the metal film 6.

As is shown in FIG. 4E, the electronic devices 4 are accommodated in thecavities 5 of the base substrate 2 and mounted on the base substrate 2(S30). FIG. 4E shows a case where the wires 8 and the electronic devices4 are connected by wire bonding using wires 7. The invention, however,is not limited to this connection method. As long as electric conductionis ensured, any connection method, such as flip chip bonding and solderbonding, is applicable.

The film thickness of the metal film 6 is limited to the range of 200angstroms to 2000 angstroms because of a relation with stability in filmformation and bonding strength. When the film thickness is 200 angstromsor less, adhesion strength between the insulator and the metal film 6 isweak. Hence, in order to ensure bonding strength, a film thickness of200 angstroms or more is necessary. Meanwhile, when the film thicknessis 2000 angstroms or more, bonding strength becomes dependent on anintermolecular bonding force of the film. This reduces an advantage ofanodic bonding.

Subsequently, as is shown in FIG. 5A, the base substrate 2 on which aremounted the electronic devices 4 and the cover substrate 3 on which isformed the metal film 6 are bonded together via the metal film 6 byanodic bonding (S31). In the case shown in FIG. 4A through FIG. 5B, thebase substrate 2 is formed in an adequate size to be superimposed on thecover substrate 3.

When anodic bonding is performed, the cover substrate 3 and the basesubstrate 2 are aligned and superimposed first. Subsequently, a negativeelectrode plate 21 made of carbon or the like is brought into contactwith the base substrate 2 on the entire surface opposite to the surfacebonded to the cover substrate 3. A positive electrode plate 22 made ofcarbon or the like is brought into contact with the cover substrate 3 onthe entire surface opposite to the surface bonded to the base substrate2. Further, a certain load is applied between the positive electrodeplate 22 and the negative electrode plate 21. In this state, thepositive electrode plate 22, the negative electrode plate 21, the basesubstrate 2, and the cover substrate 3 are heated to 200 to 300° C. by aheater or the like and a voltage of 500 to 1000 V is applied between thepositive electrode plate 22 and the negative electrode plate 21. Thebase substrate 2 and the cover substrate 3 are thus bonded together byanodic bonding.

In this state, a plurality of electronic device package elements arepresent in a single wafer obtained by bonding a wafer of base substrate2 and a wafer of cover substrate 3. Accordingly, as is shown in FIG. 5B,the electronic device packages 1 are cut off individually using a dicingsaw or a wire saw (S32). FIG. 2 shows a cross section of oneindividually cut-off electronic device package 1. In the individuallycut-off electronic device package 1, the metal film 6 is not formed onthe side surfaces of the cover substrate 3 in the thickness direction.The reason why is as follows. That is, the bonding film is formed on theentire side surfaces of the cover substrate 3 in the thickness directionin the outermost circumference portion in a state of a wafer before theelectronic device packages 1 are cut off individually. Accordingly, themetal film 6 on the bonding surface of the cover substrate 3 bonded tothe base substrate 2 and the metal film 6 on the surface opposite to theboding surface are connected on the side surfaces in the circumferenceportion. This configuration makes it possible to fix the potential ofthe metal film 6 and allows charges to migrate smoothly during anodicbonding. However, after the anodic bonding ends, the metal film 6 on theside surfaces of the cover substrate 3 in the thickness direction is nolonger necessary. Hence, in the individually cut-off electronic devicepackage 1, the metal film 6 is not formed on the side surfaces of thecover substrate 3 in the thickness direction. In other words, in theindividually cut-off electronic device package 1, the metal film 6formed entirely on one surface of the cover substrate 3 and the metalfilm 6 formed entirely on the other surface do not conduct with eachother. Thereafter, the electronic device package 1 is completed byconducting an inspection on the internal electric property (S33).

An advantage of bonding the base substrate 2 and the cover substrate 3together by anodic bonding will now be described. In a case where aceramic substrate is used as the base substrate, it is necessary to bonda cover for each individual electronic device. Accordingly, a largepressure is applied to the base substrate when the cover is bonded tothe base substrate. When the width of the bonding surface is narrow, thebonding surface cannot withstand the pressure. This causes a problemthat cracking or chipping occurs. On the contrary, because theelectronic device package 1 of this embodiment uses anodic bonding tobond the base substrate 2 and the cover substrate 3 together, aplurality of the electronic devices 4 can be mounted simultaneously.Accordingly, a pressure applied to the base substrate per package at thetime of bonding becomes small and even when the bonding surface issmall, no cracking or chipping occurs. Anodic bonding is thereforeextremely effective in manufacturing a compact package.

It should be appreciated that the scope of the invention is not limitedto the embodiment described above and various modifications can be madewithout deviating from the scope of the invention. In the embodimentdescribed above, concave portions of a rectangular shape that later formthe cavities 5 in which to accommodate the electronic devices 4 areformed in the base substrate 2 on the bonding surface to which the coversubstrate 3 is bonded. The invention, however, is not limited to thisconfiguration. For example, as is shown in FIG. 6, concave portions of arectangular shape that later form the cavities 5 in which to accommodatethe electronic devices 4 may be formed in the cover substrate 3 on thebonding surface to which the base substrate 2 is bonded. In a case wherethe cavities 5 are formed in the base substrate 2, it is difficult toform the wires 8 used to mount the electronic devices 4 on the basesubstrate 2 in some cases. In such a case, the wires 8 can be formedmore easily by forming the cavities 5 in the cover substrate 3 as isshown in FIG. 6.

One embodiment of an oscillator of the invention will now be describedwith reference to FIG. 7. As is shown in FIG. 7, an oscillator 100 ofthis embodiment includes, as a transducer electrically connected to anintegrated circuit 101, the electronic device package 1 (piezoelectrictransducer) using a piezoelectric vibrating piece made, for example, ofquartz, as the electronic device 4. The oscillator 100 includes asubstrate 103 on which an electronic component 102, such as a capacitor,is mounted. The integrated circuit 101 for oscillator is mounted on thesubstrate 103 and the electronic device package 1 (piezoelectrictransducer) is mounted thereon in the vicinity of the integrated circuit101. The electronic component 102, the integrated circuit 101, and theelectronic device package 1 (piezoelectric transducer) are electricallyinterconnected by an unillustrated wiring pattern. Each component ismolded with unillustrated resin.

In the oscillator 100 configured as above, when a voltage is applied tothe piezoelectric transducer, the piezoelectric vibrating piece in thepiezoelectric transducer vibrates. The vibration is converted to anelectric signal by the piezoelectric characteristic of the piezoelectricvibrating piece and inputted into the integrated circuit 101 as theelectric signal. The integrated circuit 101 applies various types ofprocessing to the electric signal inputted therein and outputs theresulting signal as a frequency signal. The piezoelectric transducerthus functions as an oscillator. By selectively setting theconfiguration of the integrated circuit 101 as required, for example, bysetting an RTC (Real Time Clock) module, it becomes possible to providea single-function oscillator for timepiece with an additional functionof controlling an operation date or clock time of the oscillator or anoutside device or presenting a clock time or a calendar.

1. A method for producing electronic device packages each containing anelectronic device inside, comprising: (a) defining a plurality of firstsubstrates on a first wafer and a plurality of second substrates on asecond wafer; (b) forming a bonding film on a respective oppositesurfaces of the second wafer, wherein the bonding films on the opposingsurfaces are electrically connected to each other; (c) layering, betweenboding electrodes, the first and second wafers such that at least someof the first substrates substantially coincide respectively with atleast some of the corresponding second substrates, with the bonding filmbeing placed between a respective at least some of the coinciding firstand second substrates, wherein one of the bonding electrodes on thesecond wafer is in electrical contact with the bonding films; (d)anodically bonding the first and second substrates by applying a bondingvoltage across the bonding electrodes; and (e) cutting off a respectiveat least some of packages made of coinciding first and secondsubstrates.
 2. The method according to claim 1, wherein forming abonding film on a respective opposite surfaces of the second wafercomprises forming a bonding film extensive to cover an entirety of atleast one of the opposite surfaces of the second wafer.
 3. The methodaccording to claim 1, wherein forming a bonding film on a respectiveopposite surfaces of the second wafer comprises forming a bonding filmat least in part on a side surface of the second wafer through which thebonding films formed on the opposite surfaces of the second wafer areelectrically connected to each other.
 4. The method according to claim1, wherein the bonding film has a thickness of about 200 Å to 2000 Å. 5.The method according to claim 1, wherein the bonding film is made of amaterial selected from the group consisting of Al, Si and Cr.
 6. Themethod according to claim 1, wherein forming a bonding film on arespective opposite surfaces of the second wafer comprises forming thebonding film by one of vapor deposition, sputtering and CVD.
 7. Themethod according to claim 1, wherein anodically bonding the first andsecond substrates comprises applying a voltage of about 500 V to 1000 Vacross the electrodes at a temperature of about 200° C. to about 300° C.8. The method according to claim 1, wherein the bonding films formed onopposite surfaces of the second substrate of each cut-off package areelectrically isolated from each other.
 9. The method according to claim1, further comprising a recess in at least one of a respective at leastsome of the first substrate and a respective at least some of the secondsubstrate to form a cavity for storage of the electronic device betweena respective at least some of the coinciding first and secondsubstrates.
 10. An electronic device package comprising: a hermeticallyclosed package comprising first and second substrates hermeticallybonded together; a bonding film formed on a respective opposite surfacesof the second substrate thorough which the first and second substratesare anodically bonded; and an electronic device stored inside thepackage between the first and second substrates.
 11. The packageaccording to claim 10, wherein the bonding film is extensive to cover anentirety of at least one of the opposite surfaces of the secondsubstrate.
 12. The package according to claim 10, wherein the bondingfilms formed on the opposite surfaces of the second substrate areelectrically isolated from each other.
 13. The package according toclaim 10, wherein the bonding film has a thickness of about 200 Å to2000 Å.
 14. The package according to claim 10, wherein the bonding filmis made of a material selected from the group consisting of Al, Si andCr.
 15. The package according to claim 10, wherein at least one of thefirst and second substrates is formed with a recess for storage of theelectronic device.
 16. The package according to claim 10, wherein theelectronic device is a piezoelectric transducer.
 17. An oscillatorcomprising the package defined in claim
 16. 18. An electronic devicecomprising the oscillator defined in claim 17.